In order to produce offspring, you need at least one female and one male specimen. We point this obvious fact out, because some proud boid keepers realized in their first attempt at breeding that they had unknowingly acquired two specimens of the same sex when they purchased their animals a few years ago.

It is therefore an important fact that a successful breeding starts with an appropriate selection of specimens at the point of purchase. As we already established, the best source for this is an experienced keeper. If you acquire your animals from somewhere else, and you lack the necessary experience in properly sexing the animals, an experienced keeper should accompany you when choosing your animals.

The best breeder animals will always be those that you purchased as neonates or hatchlings, and then raised yourself. The least ideal ones are wild-caught specimens. This is especially valid for fresh imports.

Male or Female Boa constrictor?

Sexing boas is one of the first skills that an aspiring breeder should acquire. It is useful to not having to rely on the skills (and honesty) of the seller when picking out offspring for future breeding projects.

Imagine that your efforts of many years are finally rewarded with a litter of newborn boids. However, when your potential customers show up, you can’t even tell the boys apart from the girls (among the snakes, not the customers).

In order to avoid this, we want to demonstrate the most common methods of gender determination in boas, as much as this is possible to do in theory:

The only method to determine the gender of young animals accurately is probing, which is done by use of a metal probe, which is available in the trade in various sizes.

When sexing the snake, a lubricated probe of adequate size is inserted into the right or left side of the cloaca, and then
gently (!) pushed towards the tip of the tail.

The probe hereby enters the hemipenial pocket of the male or the musk gland of the female. Depending on the species of boa, the probe can be inserted 2 to 5 scales deep in females, and 6 to 15 subcaudal scales (the ventral scales between the cloacae and the tip of the tail) deep in males. In order to “measure” this, place your index finger at the spot where the probe entered the cloaca, after the same has been inserted as far as possible. Afterwards, you pull out the probe and hold it on the outside of its body, right at the ventral side of the tail and count the subcaudal scales.

The previously mentioned work by Ross and Marzek contains a detailed listing of probing depths in the various species of boas on page 39 (German edition).

Another method of determining the gender in young snakes is by probing the surface of tail with your fingers. This is done by sweeping with gentle pressure from the cloaca towards the tip of the tail, using the index finger. On the upside of the tail, the thumb exercises slight counter-pressure. If the animal is a male specimen, you can feel a slight, double “crunching” when sweeping across it. This is due to the hemipenis, which is slightly moved from the pressure exerted by the index finger.

This type of sexing works with most boas. However, it is not entirely reliable. If a male specimen flexes its muscles in the tail area, the “crunching” may be absent, and the animal is then erroneously considered to be a female specimen.

Due to the increased amount of fat and muscle tissue in the tail area, it is not possible to use this method to successfully sex adult snakes. In that case, the spurs give an important hint regarding the gender of the animal, as they are much more prevalent in males.